Meaning: hard, diligent worker
Rewrite 1: works like a rottweiler gnawing on a leg
Rewrite 2: digging with all four legs and a tail
Rewrite 3: more dogged than a terrier after a rat
Rewrite 4: focused like a pointern2 on a pheasant
Rewrite 5: after a job like a sheppard on a drug bust

Comment: I don’t know many dogs that actually do “work,” so maybe it’s the right time to rewrite this dog of a cliché. I tried to stick with dogisms for this cliché, focusing on breeds that work hard at their specialty.

More reading about clichés
What I found when I googled “clichés”:
• Boing Boing: TV clichés catalogued by BoingBoing, “a directory of wonderful things.”